Various components of conventional drill pipe, coiled tubing or other down hole tools may get stuck in the well bore at times. Jars are used in the oilfield industry to deliver jarring blows to a tubing string in order to free a stuck component, such as a stuck section of pipe. Jars are also used in fishing operations, in order to collect and free a object stuck in a downhole well. Under these circumstances, repetitive upjarring or downjarring with a jarring tool can be useful. Double-acting jars exist that are capable of performing this function to a most degree, although many traditional double-acting jars can only perform sequential up and down jars.
Adapting a jar tool to a coiled tubing application presents some challenges to overcome. A coiled tubing operation may involve a continuous pipe or tubing, which is uncoiled from a reel as it is lowered into the well bore, and can be used in drilling or workover applications for example. However, coiled tubing presents a number of working constraints to the design of a tool. First of all, due to the limited strength of the coiled tubing, limited compressive loads can be placed on the tubing by the rig operator. Essentially, this means that downhole tools which require compressive force to operate, such as a jarring tool, must be capable of operating with the limited compressive load capability of coiled tubing. In addition, in coiled tubing applications the overall length of the downhole tool becomes significant since there is limited distance available at the wellhead, for example between the stuffing box and the blowout preventor, to accommodate the bottom hole assembly. A typical bottom hole assembly may include additional tools, for example, a quick disconnect, a sinker bar, a release tool of some type, and an overshot. Thus, the length of the jarring tool itself becomes particularly significant since the entire bottom hole assembly may be required to fit within the limited distance between the stuffing box and blowout preventor to introduce it into a pressurized well. Furthermore, within these confines, the jarring tool may be required to have a large enough internal bore to permit pump-down tools to pass. Thus, the coiled-tubing jarring tool may have a limited overall wall thickness in view of limited outer diameter conditions.